A prior-art joint of this type according to U.S. Pat. No. 5,100,254 has, among other things, a rubber bellows with a metal ring of a U-shaped cross section, which is connected thereto and in the U-shaped recess of which the lip of a protective cap consisting of plastic is clipped. Since the protective cap must be pushed against the rubber bellows downwardly in the direction of the longitudinal direction to clip this lip into the ring of the rubber bellows, the rubber bellows is inevitably subject to an undesired deformation, because an opposing pressing force with a counterpressure element is absent. Consequently, the protective cap with the compressed rubber bellows must be inevitably pulled in the opposite direction after the clipping, which may in turn lead to the release of the protective cap from the ring. At any rate, it is disadvantageous in the different embodiments according to this document that the protective cap must always be pressed in the direction of the longitudinal axis towards the ball against the rubber bellows for connection with the ring. An undesired deformation of the rubber bellows is inevitable as a consequence of these axial forces.
A joint of a different type, which is surrounded by a protective cap fastened to the joint housing of the ball-and-socket joint, has become known from EP 0 570 736 A1. This protective cap is held in a recess extending circularly around the joint housing by means of a retaining ring. Even though this construction advantageously shields the rubber bellows against lateral thermal effects like a heat shield, the penetration of particles from the pivot side toward the rubber bellows cannot be prevented, because the necessary angular deflection of the ball pivot inevitably determines the size of the non-shielded intermediate space between it and the inner side of the protective cap. In addition, this construction requires two different fastenings, namely, for the rubber bellows, on the one hand, and for the protective shield, on the other hand.
Such heat insulation means are always needed whenever ball-and-socket joints are arranged in the vicinity of heat sources, e.g., disk brakes, without sufficient protection being provided for cooling or without other heat-insulating measures being able to be taken. Protective caps made of sheet metal have been known in this connection, which are arranged either at the steering knuckle, at the joint housing of the ball pivot or at the suspension arm. They are mounted in the course of the mounting of the axle or the mounting of the individual components. The drawback of all these solutions is based especially on their complicated and error-prone mounting or, in the case of the solutions with arrangement at the joint housing, on the strong effect of the movements of the joint on the possible enclosing angle of the sheet metal around the sealing bellows. Joints with a large angular deflection can therefore be protected only insufficiently with the solution according to EP 0 570 736 A1.
Protective caps made of plastic or rubber materials can withstand only substantially lower peak temperatures than metal or, in the case of rubber material, they may even be deformed by the relative wind of the vehicle and/or be subject to fluttering movements.
By contrast, caps made, of metal or plastic, which are pressed on the pivot pin, must be oriented during mounting in the vehicle and are associated with the risk of becoming separated due to the short length over which they are pressed on.
To illustrate these problems, reference is made to the work of Prof. Jörnsen Reimpell, Cert. Eng., entitled “Chassis Engineering: Wheel Suspensions,” 2nd edition; 1988, pp. 132 and 304, in which joints with protective caps are shown on the front axle side of a motor vehicle.